Towards sustainable ground improvement: A life cycle assessment of stone columns and dry soil mixing in Norwegian clays-Paper

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The VIBE project assessed vibro-replacement (stone columns) as a potentially lower-carbon alternative to dry deep soil mixing (DSM) in Norwegian soft clays. Stone columns use compacted granular material, while DSM mixes clay with cementitious binders such as lime and cement.<br /><br />Field trials at Onsøy tested primary and recycled aggregates. Unexpected highly sensitive “quick” clay caused softening and liquefaction during installation, preventing successful column installation. The trials nevertheless produced valuable monitoring data and highlighted the need for thorough, well-distributed soil investigations before using vibro-replacement.<br /><br />The researchers calculated emissions from transport, materials and fuel using the EFFC carbon calculator and a modified version with Scandinavian emission factors. For the completed test-site work, estimated emissions were about 123–127 kg CO₂-equivalent per square metre. Transport distances, machinery and fuel were important contributors. Recycled aggregates can lower impacts, but their benefits depend partly on processing and transport.<br /><br />A separate, fictional comparison assumed equivalent ground-improvement performance, shorter transport distances and recycled aggregates used without additional processing. Under those assumptions, vibro-replacement emitted an estimated 73.7 kg CO₂-equivalent/m², compared with 240.8 kg/m² for DSM—more than three times as much. The difference was mainly due to emissions from producing the lime and cement used in DSM. If recycled aggregate preparation had no emissions, DSM’s footprint would be about five times higher.<br /><br />Overall, vibro-replacement shows promise as a lower-carbon option for Scandinavian clays, provided site conditions are suitable and aggregate sourcing and transport are managed carefully. The authors also found only minor differences between the two carbon calculators, suggesting the EFFC tool is suitable for Norwegian assessments.

Keywords

vibro-replacement

stone columns

dry deep soil mixing

soft clay

quick clay

carbon emissions

recycled aggregates

ground improvement

Norwegian soils

EFFC carbon calculator